Hybrid tire cord and method for manufacturing the same

ABSTRACT

Disclosed are a hybrid tire cord, which can be easily manufactured and has more uniform physical properties, and improved strength and fatigue resistance, and a method for manufacturing the same. The hybrid tire cord includes a nylon primarily twisted yarn and an aramid primarily twisted yarn, wherein the nylon primarily twisted yarn and the aramid primarily twisted yarn are secondarily twisted together, and after untwisting of the secondary twisting of the hybrid tire cord having a predetermined length, a length of the aramid primarily twisted yarn is 1.005 to 1.025 times a length of the nylon primarily twisted yarn.

TECHNICAL FIELD

The present invention relates to a hybrid tire cord includingheterogeneous yarns having different physical properties and a methodfor manufacturing the same. More specifically, the present inventionrelates to a hybrid tire cord which can be easily manufactured and hasmore uniform physical properties, and improved strength and fatigueresistance and a method for manufacturing the same.

BACKGROUND ART

Tire cords, especially, tire cords treated with an adhesive agent,referred to as “dip cords”, are widely used as reinforcing materials ofrubber products such as tires, conveyor belts, V-belts and hoses andmaterials for tire cords include nylon fibers, polyester fibers, rayonfibers and the like. One of essential methods of improving performanceof final rubber products is to improve physical properties of tire cordsused as reinforcing materials.

Improved vehicle performance and road conditions have brought aboutgradually increasing vehicle driving speed. Accordingly, a great deal ofresearch is underway on tire cords capable of maintaining stability anddurability of tires even during high-speed driving.

A tire cord is classified depending on used part and rule and is dividedinto a carcass for entirely supporting the tire, a belt for supportingload upon high-speed driving and a cap ply for preventing deformation ofthe belt. Recently, improved highway conditions have resulted inincreased vehicle speeds, causing problems such as deformation of thebelt of the tire and deterioration in drive comfort. For this reason,importance of a cap ply to prevent deformation of the belt isincreasing.

Major materials for currently used tire cords for cap ply are nylon andaramid. Of them, nylon is applied to most tires due to low cost,superior adhesivity and superior fatigue resistance as compared to othermaterials. In addition, nylon has a high compressive stress which isadvantageous for preventing deformation of belts during high-speeddriving. However, nylon has a problem of causing flat spots due to lowmodulus and great deformation with variation in temperature.

Aramid used as another material for the cap ply, in addition to thenylon, has almost no flat spot phenomenon in which a tire is deformedupon parking for a long time due to very high modulus and less change inmodulus at room temperature and high temperature and is thus generallyfor high-quality tire essentially requiring high quality. However,aramid is inapplicable to general-purpose tires because it is veryexpensive. In addition, aramid has drawbacks of relative difficulty intire molding due to high modulus, and low fatigue resistance anddurability due to low breaking elongation.

In order to solve the aforementioned problems of nylon and aramid, ahybrid cord to which both nylon and aramid are applied has beendeveloped. In particular, a hybrid cord having a structure in which anylon primarily twisted yarn is covered with an aramid primarily twistedyarn (hereinafter, “covering structure”) has been developed.

Typically, in order to allow the aramid primarily twisted yarn and thenylon primarily twisted yarn to be simultaneously broken, the aramidfilament yarn having a higher modulus is primarily twisted at a greatertwist number as compared to the nylon filament yarn having a lowermodulus and, in order to prevent aggregation between primarily twistedyarns during secondary twisting, the aramid filament yarn and the nylonfilament yarn are primarily twisted in different directions. Forexample, an aramid primarily twisted yarn is produced by primarilytwisting the aramid filament yarn at a high twist number in anS-direction, a nylon primarily twisted yarn is produced by primarilytwisting the nylon filament yarn at a low twist number in a Z-direction,and a 2-ply yarn having a covering structure is produced by secondarilytwisting the aramid primarily twisted yarn and the nylon primarilytwisted yarn at a low twist number in an S-direction.

The 2-ply yarn having a covering structure described above has drawbacksof low production efficiency and high manufacturing cost because it isproduced by a three-step process using a ring twister (that is, a firststep of primarily twisting an aramid filament yarn to form an aramidprimarily twisted yarn, a second step of primarily twisting a nylonfilament yarn to form a nylon primarily twisted yarn, and a third stepof secondarily twisting the aramid primarily twisted yarn and the nylonprimarily twisted yarn).

In addition, there are problems of high deviation in physical propertiesand increased defect rate in the manufacture of the hybrid cord, becausethe aramid primarily twisted yarn for covering the nylon primarilytwisted yarn is pulled by friction with a guide or roller to form aroof, or the nylon primarily twisted yarn is compressed, thus causingshape non-uniformity, during drying and thermal treatment after dippingthe 2-ply yarn having a covering structure in an adhesive agentsolution.

In addition, because the aramid filament yarn is primarily twisted at ahigher twist number as compared to the nylon filament yarn in order tominimize the difference in physical properties between nylon and aramid,strength of the aramid filament yarn is greatly deteriorated and theadvantage, i.e., high modulus, of the aramid cannot be secured. As aresult, the hybrid cord having a covering structure inevitably has lowstrength as expected and thus has a relatively high risk of tiredeformation during high-speed driving.

In order to solve the aforementioned disadvantages of the hybrid cordhaving a covering structure, Korean Patent Laid-open No.10-2014-0090307, registered to the present applicant, suggests a hybridcord having a merge structure which is produced by secondarily twistinga nylon primarily twisted yarn and an aramid primarily twisted yarn,which have been primarily twisted in the same direction, in a directionopposite to the direction, wherein secondary twisting is conducted suchthat the nylon and aramid primarily twisted yarns have an identicalstructure.

However, in the case of a hybrid cord having a merge structure, stressis intensely applied to the aramid primarily twisted yarn upon repeatedtension and compression of tires, thus inevitably causing low fatigueresistance of tire cord and, disadvantageously, resulting inimpossibility of securing safety of tires during long-term high-speeddriving.

DISCLOSURE Technical Problem

Therefore, the present invention has been made in view of the problemsresulting from limitations and drawbacks of the related art and providesa hybrid tire cord and a method for manufacturing the same.

It is one aspect of the present invention to provide a hybrid tire cordwhich can be easily manufactured and is applicable to ultra-highperformance tires due to high strength and fatigue resistance.

It is another aspect of the present invention to provide a method ofmanufacturing a hybrid tire cord, which is applicable to ultra-highperformance tires due to high strength and fatigue resistance, at highproduction efficiency and low cost, while minimizing deviation inphysical properties.

The aspects of the present invention as described above as well as otherfeatures and advantages of the present invention will be described inthe following or will be clearly understood by those skilled in the artfrom the description. The aspects and other advantages of the presentinvention can be implemented and accomplished by configurationsspecified in the Detailed Description of the Invention and Claims

Technical Solution

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a hybrid tire cordincluding a nylon primarily twisted yarn, and an aramid primarilytwisted yarn, wherein the nylon primarily twisted yarn and the aramidprimarily twisted yarn are secondarily twisted together, and afteruntwisting (post-untwist) of the secondary twisting of the hybrid tirecord having a predetermined length, a length of the aramid primarilytwisted yarn is 1.005 to 1.025 times a length of the nylon primarilytwisted yarn.

The nylon primarily twisted yarn may have a first twist direction, thearamid primarily twisted yarn may have a second twist direction, thenylon primarily twisted yarn and the aramid primarily twisted yarn maybe secondarily twisted together in a third twist direction, the secondtwist direction may be the same as the first twist direction, and thethird twist direction may be opposite to the first twist direction.

The aramid primarily twisted yarn may have a lower twist number than atwist number of the nylon primarily twisted yarn.

The aramid primarily twisted yarn may have a 0.1 to 5% lower twistnumber than a twist number of the nylon primarily twisted yarn.

A weight ratio of the nylon primarily twisted yarn to the aramidprimarily twisted yarn may be 20:80 to 80:20.

The hybrid tire cord may further include an adhesive agent coated on thenylon primarily twisted yarn and the aramid primarily twisted yarn,wherein strength at break and elongation at break measured by ASTM D885are 8.0 to 15.0 g/d and 7 to 15%, respectively, the twist number of thearamid primarily twisted yarn is 0.1 to 5% lower than the twist numberof the nylon primarily twisted yarn, based on 100, the twist number ofthe nylon primarily twisted yarn, and a strength maintenance percentageafter disk fatigue test conducted by JIS-L 1017 of Japanese StandardAssociation (JSA) is 90% or higher.

The hybrid tire cord may have 3% LASE, 5% LASE, and 7% LASE measured byASTM D885, of 0.8 to 2.0 g/d, 1.5 to 4.0 g/d, and 3.0 to 6.0 g/d,respectively.

The hybrid tire cord may have a shrinkage of 1.5 to 2.5%, wherein theshrinkage is measured under a primary load of 0.01 g/denier at 180° C.for 2 minutes.

In another aspect of the present invention, provided is a method ofmanufacturing a hybrid tire cord including: a first step of primarilytwisting an aramid filament yarn in a first direction to form an aramidprimarily twisted yarn; a second step of primarily twisting a nylonfilament yarn in a second direction to form a nylon primarily twistedyarn, the second step and the first step being conducted simultaneously,and a third step of secondarily twisting the aramid primarily twistedyarn and the nylon primarily twisted yarn in a third direction to form aplied yarn, the third step being conducted continuously with the firstand second steps, wherein the first, second and third steps areconducted by one twister, the second direction is the same as the firstdirection, the third direction is opposite to the first direction,tension applied to the nylon filament yarn in the second step is higherthan tension applied to the aramid filament yarn in the first step, andthe tension applied to the nylon filament yarn in the second step ishigher than the tension applied to the aramid filament yarn in the firststep in such an amount that the aramid primarily twisted yarn is 1.005to 1.025 times longer than the nylon primarily twisted yarn afteruntwisting of the secondary twist of the hybrid tire cord with apredetermined length.

The method may further include dipping the plied yarn in an adhesiveagent solution, drying the adhesive agent solution-impregnated pliedyarn, and thermally treating the dried plied yarn.

The dipping, drying and thermal treatment steps may be continuouslyconducted, and tension applied to the plied yarn in the dipping, dryingand thermal treatment steps may be 0.4 g/d or less per cord.

General description related to the present invention given above servesto illustrate or disclose the present invention and should not beconstrued as limiting the scope of the present invention.

Effects of the Invention

According to the present invention, secondary twisting and primarytwisting are conducted in one twister, thereby improving productionefficiency of the hybrid tire cord and reducing manufacturing coststhereof.

In addition, the twist number of the primary twisting of the aramidfilament yarn is much lower than the twist number of aramid primarytwisting in the covering structure of the prior art, thereby greatlyreducing deterioration in strength of aramid. That is, in manufacture ofthe hybrid tire cord, relatively high strength of aramid can bemaintained, and the hybrid tire cord of the present invention canminimize tire deformation during high-speed driving owing to highstrength of aramid.

In addition, the hybrid tire cord of the present invention has a stablestructure in which the aramid primarily twisted yarn and nylon primarilytwisted yarn are twisted in a substantially identical ratio, therebyminimizing deviation in physical properties and defect rate which may becaused in the manufacturing process, as compared to the prior artassociated with a covering structure.

In addition, according to the present invention, after untwisting thecord, the length of aramid primarily twisted yarn is 1.005 to 1.025times the length of nylon primarily twisted yarn, thereby dispersingstress applied to the hybrid tire cord during repetition oftension/compression of the tire to the aramid primarily twisted yarn aswell as the nylon primarily twisted yarn. Consequently, the hybrid tirecord of the present invention having superior fatigue resistance canmaintain stability of tires even during long-term high-speed driving. Inparticular, difference in fatigue resistance occurs whentension/compression deformation is serious, and difference in fatigueresistance is further increased when tension/compression/shearing isrepeatedly applied upon actual tire driving.

BEST MODE

Hereinafter, embodiments of the hybrid tire cord of the presentinvention and a method for manufacturing the same will be described indetail with reference to the annexed drawings.

Those skilled in the art will appreciate that various modifications,additions and substitutions are possible, without departing from thescope and spirit of the invention as disclosed in the accompanyingclaims. Accordingly, the present invention includes modifications andalterations which fall within the scope of the inventions as claimed andequivalents thereto.

The term “primarily twisted yarn” as used herein refers to a single yarnmade by twisting one filament yarn in one direction.

The term “plied yarn” as used herein refers to a yarn made by twistingtwo or more primarily twisted yarns together in one direction, which isalso called a “raw cord”.

The term “tire cord” as used herein includes the “raw cord” as well as“dip cord” which means a plied yarn containing an adhesive agent so thatit can be directly applied to rubber products. An adhesiveagent-containing fabric which is produced by spinning plied yarns,making a fabric with the yarns and then dipping the fabric in anadhesive agent solution is also included in the tire cord.

The term “twist number” used herein means the number of twists per onemeter and its unit is TPM (twist per meter).

The tire cord according to the present invention is a hybrid type ofnylon and aramid, which includes a first twist direction of nylonprimarily twisted yarns and a second twist direction of aramid primarilytwisted yarns wherein the nylon primarily twisted yarns and the aramidprimarily twisted yarns are together secondarily twisted in a thirdtwist direction.

The nylon filament yarns and the aramid filament yarns aresimultaneously respectively primarily twisted in one twister (forexample, a cable cord twister), thereby forming the nylon primarilytwisted yarn and the aramid primarily twisted yarn. For this reason, thesecond twist direction of the aramid primarily twisted yarns is the sameas the first twist direction of the nylon primarily twisted yarns andthe third twist direction (that is, secondary twisting direction) isopposite to the first twist direction.

According to the present invention, because primary twisting andsecondary twisting are conducted by one twister, production efficiencyof the hybrid tire cord can be improved and manufacturing costs can bereduced.

Meanwhile, according to the present invention, although primary twistingand secondary twisting are conducted by one twister, regarding apredetermined length of the hybrid tire cord, after the secondary twistis untwisted, the length of the aramid primarily twisted yarn is 1.005to 1.025 times the length of the nylon primarily twisted yarn. That is,the hybrid tire cord of the present invention has a merge structurehaving a partial covering structure.

Accordingly, unlike a hybrid tire cord having a merge structure in whichnylon primarily twisted yarns and aramid primarily twisted yarns havesubstantially identical length and identical structure (that is, afteruntwisting of secondary twisting, the length of the aramid primarilytwisted yarn is 1.005 times lower than the length of the nylon primarilytwisted yarn), in the hybrid tire cord of the present invention, stressapplied to a hybrid tire cord upon repeated tension/compression of atire can be dispersed to not only the aramid primarily twisted yarn, butalso the nylon primarily twisted yarn. As a result, the hybrid tire cordof the present invention having superior fatigue resistance can maintainstability of tires even upon rapid driving for a long time.

Meanwhile, when the length of the aramid primarily twisted yarns afteruntwisting of secondary twisting exceeds 1.025 times the length of nylonprimarily twisted yarns, the hybrid tire cord has a similar unstablestructure to the covering structure of the prior art, thus increasingdeviation of physical properties and defect rate during manufacture forthe aforementioned reasons and tire defect rate due to deviation ofphysical properties during tire manufacture.

According to an embodiment of the present invention, the aramidprimarily twisted yarn of the hybrid tire cord has lower a twist numberthan that of the nylon primarily twisted yarn. For example, the twistnumber of aramid primarily twisted yarns may be 0.1 to 5% lower thanthat of the nylon primarily twisted yarns.

Because the twist number of primary twisting of aramid filament yarns ismuch less than the twist number of primary twisting of aramid (which ismuch greater than the twist number of primary twisting of nylon) in thecovering structure of the prior art, the hybrid tire cord of the presentinvention has less deterioration in strength of aramid. That is, in theprocess of manufacturing the hybrid tire cord, relatively high strengthof aramid can be maintained and the hybrid tire cord of the presentinvention can minimize deformation of tires during high-speed drivingtire owing to high strength of aramid.

The nylon used for manufacturing the hybrid tire cord of the presentinvention contains a highly polar amide group in a main chain and iscrystalline due to tacticity and chirality thereof. Nylon is commonnylon 6, nylon 66, or nylon 6.10, preferably nylon 66.

The nylon filament yarn used for manufacturing the hybrid tire cord ofthe present invention is not particularly limited and has preferably afineness of 400 to 3000 denier, tensile strength of 8 g/d or higher, anda breaking elongation of 17% or higher. When the nylon filament yarn hasa tensile strength less than 8 g/d, movement of belts during vehiclerunning cannot be sufficiently prevented, or when a great amount ofcords is used to prevent this phenomenon, weight of tires is increased.When breaking elongation of the nylon filament yarn is less than 17%,serious strength deterioration resulting from repetition oftension/compression of tires occurs due to bad fatigue resistance oftire cords.

Aramid contains an amide group and a phenyl group in a main chain andthus has a modulus 10 times or higher than nylon. Aramid is classifiedinto para (p-) and meta (m-) aramid depending on bonding positions of aphenyl group and is preferably poly(p-phenylene terephthalate)represented by the following Formula 1:

wherein n is determined depending on molecular weight of aramid and isnot particularly limited in the present invention.

According to an embodiment of the present invention, the aramid filamentyarn has a fineness of 400 to 3000 denier, a tensile strength of 20 g/dor higher and a breaking elongation of 3% or higher. When the tensilestrength of the aramid filament yarn is less than 20 g/d, low strengthof nylon filament yarn cannot be sufficiently compensated for and thereis thus an increased risk of causing tire deformation during high-speeddriving.

In the hybrid tire cord according to an embodiment of the presentinvention, the weight ratio of nylon primarily twisted yarns to aramidprimarily twisted yarns is 20:80 to 80:20.

When the weight of nylon primarily twisted yarns exceeds 4 times theweight of aramid primarily twisted yarns, physical properties of finallyobtained hybrid tire cords become similar to those of nylon and flatspots thus occur. On the other hand, if the weight of aramid primarilytwisted yarns exceeds 4 times the weight of nylon primarily twistedyarns, strength of hybrid tire cords is improved, but shrinkage islowered and movement of belts during vehicle running cannot besufficiently prevented, it is difficult to secure durability of tiresdue to deteriorated fatigue resistance, and costs are increased due touse of great amount of expensive aramid.

The hybrid tire cord according to an embodiment of the present inventionmay further include an adhesive agent coated on the nylon primarilytwisted yarn and the aramid primarily twisted yarn in order to improveadhesivity to tires and strength at break, elongation at break measuredby ASTM D885 may be 8.0 to 15.0 g/d and 7 to 15%, respectively, andstrength maintenance percentage after disk fatigue test conducted byJIS-L 1017 of Japanese Standard Association (JSA) may be 90% or higher.In addition, the hybrid tire cord may have 3% LASE, 5% LASE, and 7% LASEmeasured by ASTM D885 of 0.8 to 2.0 g/d, 1.5 to 4.0 g/d, and 3.0 to 6.0g/d, respectively. The hybrid tire cord may have a shrinkage of 1.5 to2.5%, wherein the shrinkage is measured under a primary load of 0.01g/denier at 180° C. for 2 minutes.

Hereinafter, the method for manufacturing the hybrid tire cord of thepresent invention as mentioned above will be described in more detail.

Both aramid filament yarns having a fineness of 400 to 3,000 denier andnylon filament yarns having a fineness of 400 to 3,000 denier areintroduced into a cable cord twister for conducting both primarytwisting and secondary twisting. In the twister, a first step of primarytwisting an aramid filament yarn in a first direction to form an aramidprimarily twisted yarn and a second step of primary twisting a nylonfilament yarn in a second direction to form a nylon primarily twistedyarn are simultaneously conducted, and a third step of secondarytwisting the aramid primarily twisted yarn and the nylon primarilytwisted yarn in a third direction to form a plied yarn is continuouslyconducted with the first and second steps. As described above, thesecond direction is the same as the first direction and the thirddirection is opposite to the first direction.

According to the present invention, because a plied yarn is produced bya continuous process of conducting both primary twisting and secondarytwisting in one twister, production efficiency of hybrid tire cord canbe improved, as compared to a conventional batch process of conductingprimary twisting of nylon filament yarns and aramid filament yarns inseparate twisters and then conducting secondary twisting using anothertwister.

According to the present invention, tension applied to the aramidfilament yarn in the second step is greater than tension applied to thearamid filament yarn in the first step. Accordingly, although primarytwisting and secondary twisting are conducted by one twister, the lengthof the aramid primarily twisted yarn after untwisting of secondarytwisting in the hybrid tire cord with a predetermined length may beslightly longer than that of the nylon primarily twisted yarn. As aresult, stress applied to the hybrid tire cord during repetition oftension/compression of the tire can be dispersed to not only the aramidprimarily twisted yarn, but also to nylon primarily twisted yarn and thehybrid tire cord can maintain stability of the tire even during drivingdue to superior fatigue resistance.

In addition, because tension applied to the nylon filament yarn ishigher than tension applied to the aramid filament yarn, although onetwist number of primary twisting and secondary twisting is set at thetwister, the twist number of the aramid primarily twisted yarn may beslightly different from the twist number of the nylon primarily twistedyarn.

According to an embodiment of the present invention, tension applied tothe nylon filament yarn in the second step is higher than tensionapplied to the aramid filament yarn in the first step and the differencetherebetween may make the length of the aramid primarily twisted yarn1.005 to 1.025 times the length of the nylon primarily twisted yarnafter untwisting of secondary twisting with respect to the hybrid tirecord with a predetermined length (that is, after untwisting of the pliedyarn).

The levels of tension applied to the nylon filament yarn and the aramidfilament yarn can be controlled by suitably setting revolutions perminute (rpm) of rolls of the twister.

In an embodiment related to production of a dip cord, not a raw cord,dipping the plied yarn in an adhesive agent solution, drying theadhesive agent solution-impregnated plied yarn and thermally treatingthe dried plied yarn may be continuously conducted in order to improveadhesivity to tires.

A resorcinol formaldehyde Latex (RFL) solution, an epoxy adhesivesolution or the like can be used as the adhesive agent solution.

The drying temperature and time of the adhesive agent solution may bechanged according to composition and the drying is commonly at 100 to200° C. for 30 to 120 seconds.

The thermal treatment may be conducted at 200 to 250° C. for 30 to 120seconds.

Meanwhile, although the twister is set to conduct the same twist numberof primary twisting and secondary twisting, in the process of dippingand then drying the plied yarn produced by the twister, untwisting mayoccur. In order to prevent this phenomenon, in the continuouslyconducted dipping, drying and thermal treatment steps, tension appliedto the plied yarn is preferably 0.4 g/d or less per cord.

Hereinafter, the present invention will be described in more detail withreference to the following examples and comparative Examples. Thefollowing examples are only given for better understanding of thepresent invention and should not be construed as limiting the scope ofthe present invention.

Production of Plied Yarn (Raw Cord)

EXAMPLE 1

A nylon filament yarn having a fineness of 1,260 denier and an aramidfilament yarn having a fineness of 1,500 denier were introduced into acable cord twister and Z-direction of primary twisting and S-directionof secondary twisting were simultaneously conducted to produce a 2-plyyarn. At this time, the cable cord twister was set to a twist number of300 TPM for primary twisting and secondary twisting, and tension appliedto the nylon filament yarn was 52%, and tension applied to the aramidfilament yarn was 2.5 position in the production.

EXAMPLE 2

A plied yarn was produced in the same manner as in Example 1, exceptthat the tension applied to the nylon filament yarn was 52% and thetension applied to the aramid filament yarn was 2.25 position.

EXAMPLE 3

A plied yarn was produced in the same manner as in Example 1, exceptthat the tension applied to the nylon filament yarn was 52% and thetension applied to the aramid filament yarn was 2.0 position.

EXAMPLE 4

A plied yarn was produced in the same manner as in Example 1, exceptthat the tension applied to the nylon filament yarn was 52% and thetension applied to the aramid filament yarn was 1.5 position.

COMPARATIVE EXAMPLE 1

A plied yarn was produced in the same manner as in Example 1, exceptthat the tension applied to the nylon filament yarn was 52% and thetension applied to the aramid filament yarn was 3.25 position.

COMPARATIVE EXAMPLE 2

A plied yarn was produced in the same manner as in Example 1, exceptthat the tension applied to the nylon filament yarn was 52% and thetension applied to the aramid filament yarn was 2.75 position.

COMPARATIVE EXAMPLE 3

A plied yarn was produced in the same manner as in Example 1, exceptthat the tension applied to the nylon filament yarn was 52% and thetension applied to the aramid filament yarn was 0.75 position.

Regarding plied yarns respectively produced in Example 1 to 4 andComparative Example 1 to 3, a ratio of length of aramid primarilytwisted yarn to length of nylon primarily twisted yarn was obtained bythe following method and results are shown in Table 1.

Ratio of Length of Aramid Primarily Twisted Yarn to Length of NylonPrimarily Twisted Yarn

A load of 0.05 g/d was applied to a 25 cm length plied yarn sample tountwist secondary twists and separate them from each other. Then, first,a nylon primarily twisted yarn was removed by cutting, the length ofaramid primarily twisted yarn to which a load of 0.05 g/d was appliedwas measured, untwisting of the secondary twists was repeated, thearamid primarily twisted yarn was removed by cutting, and the length ofnylon primarily twisted yarn to which a load of 0.05 g/d was applied wasmeasured. A ratio of length of aramid primarily twisted yarn to lengthof nylon primarily twisted yarn was calculated by the following Equation1:

R=La/Ln   <Equation1>:

wherein R is a ratio of a length of an aramid primarily twisted yarn toa length of a nylon primarily twisted yarn, La is a length of an aramidprimarily twisted yarn, and Ln is a length of a nylon primarily twistedyarn.

TABLE 1 Aramid Nylon Aramid primarily twisted yarn tension tensionlength/nylon primarily twisted yarn (position) (%) length Example 1 2.552 1.005 Example 2 2.25 52 1.01 Example 3 2.0 52 1.02 Example 4 1.5 521.025 Comparative 3.25 52 1 Example 1 Comparative 2.75 52 1.003 Example2 Comparative 0.75 52 1.03 Example 3

Production of Dip Cord

EXAMPLE 5

2-ply yarn of Example 1 was dipped in a resorcinol-formaldehyde-latex(RFL) adhesive agent solution containing 2.0 wt % of resorcinol, 3.2 wt% of formalin (37%), 1.1 wt % of sodium hydroxide (10%), 43.9 wt % ofstyrene/butadiene/vinyl pyridine (15/70/15) rubber (41%), and water. The2-ply yarn containing the RFL solution introduced by dipping was driedat 150° C. for 100 seconds and thermally treated at 240° C. for 100seconds to complete a dip cord. Tension applied to the 2-ply yarn in thedipping, drying and thermal treatment processes was controlled to 0.5kg/cord.

EXAMPLES 6 to 8

Dip cords were produced in the same manner as in Example 5, except thatplied yarns of Examples 2 to 4 were used, instead of 2-ply yarn ofExample 1.

COMPARATIVE EXAMPLES 4 to 6

Dip cords were produced in the same manner as in Example 5, except thatplied yarns of Comparative Examples 1 to 3 were used, instead of 2-plyyarn of Example 1.

Strength at break and non-uniformity thereof, elongation at break andnon-uniformity thereof, shrinkage, and disk fatigue characteristics ofdip cords obtained by Examples 5 to 8 and Comparative Examples 4 to 6were measured by the following methods and results are shown in Table 2.

Strength at Break and Non-Uniformity Thereof & Elongation at Break andNon-Uniformity Thereof

Strength at break and elongation at break of the dip cord were measuredusing an Instron tester (Engineering Corp., Canton, Mass.) by applying atensile speed of 300 m/min to ten 250 mm samples in accordance with theASTM D-885 test method. Subsequently, strength at break (g/d) of eachsample was obtained by dividing strength at break of each sample by thetotal fineness of the dip cord. Subsequently, averages of strength atbreak and elongation at break of ten samples were calculated to obtainstrength at break and elongation at break of the dip cord.

Meanwhile, the differences in maximum and minimum between strengths atbreak of ten samples were calculated and the differences in maximum andminimum between elongations at break of the samples were calculated toobtain non-uniformity of strength at break and non-uniformity ofelongation at break of the dip cord.

Shrinkage (%)

Shrinkage was measured using Testrite equipment under a primary load of0.01 g/De at 180° C. for 2 minutes after allowing to stand underatmospheric conditions of a temperature of 25° C. and a relativehumidity of 65% for 24 hours or longer.

Disk Fatigue Characteristics

The hybrid tire cord, strength (strength before fatigue) of which hadbeen measured, was vulcanized to a rubber to produce a sample andtension and compression were repeated for 16 hours within the range of±2% and +3/-10% while rotating at 80° C. and at a speed of 2,500 rpmusing a disk fatigue tester in accordance with JIS-L 1017 of JapaneseStandard Association (JSA), to apply fatigue to the sample. Then, therubber was removed from the sample and strength after fatigue of thehybrid tire cord was then measured. Strength maintenance percentagedefined by the following Equation 2 was calculated based on strengthbefore fatigue and strength after fatigue:

Strength maintenance percentage (%)=[strength after fatigue(kgf)/strength before fatigue (kgf)]×100   <Equation 2>

wherein strength before fatigue and strength after fatigue (kgf) areobtained by measuring strength at break of the hybrid tire cord whileapplying a tensile speed of 300 m/min to a 250 mm sample using anInstron tester (Instron Engineering Corp., Canton, Mass.) in accordancewith ASTM D-885.

Bending Fatigue Characteristics

Bending fatigue test, which is a simulated test oftension/compression/shearing deformation which occurs during tiredriving, was used. A 0.6 mm rubber was stacked on two cord layers, i.e.,upper and lower cord layers, with a gap of 25 EPI (End per Inch) suchthat the total thickness reaches 5 mm, vulcanized at 160° C. for 20minutes to produce a sample and a warp yarn direction of width was cutto 1 inch to produce a fatigue test sample. At this time, a load of 68kgf was repeatedly applied 37500 cycles at a spindle of 0.5 inches atroom temperature, 10 cords were then collected and strength afterfatigue of the cords was measured. At this time, strength before fatigueand strength after fatigue (kgf) were obtained by measuring strength atbreak of the hybrid tire cord while applying a tensile speed of 300m/min to a 250 mm sample using an Instron tester (Instron testerEngineering Corp., Canton, Mass.) in accordance with ASTM D-885.

TABLE 2 Comparative Comparative Comparative Example 5 Example 6 Example7 Example 8 Example 4 Example 5 Example 6 Aramid 1.005 1.01 1.02 1.025 11.003 1.03 primarily twisted yarn length/nylon primarily twisted yarnlength Strength at break (g/d) 13.4 13.5 13.9 13.1 13.7 12.8 12.6Strength at break 0.3 0.4 0.4 0.4 0.3 0.3 6.5 non-uniformity (g/d)Elongation at break (%) 11.0 11.3 11.8 11.9 10.8 10.8 12.5 Elongation atbreak 1.6 1.8 1.8 2.0 1.4 1.6 4.0 non-uniformity (%) Shrinkage (%) 2.02.1 2.1 2.0 2.5 2.0 2.0 Disk fatigue ±2% 96 96 98 95 87.9 92 94.5strength maintenance percentage (%) Disk fatigue +3/−10% 90.5 91.6 92.593.1 78.5 80.2 82.4 strength maintenance percentage (%) Bending fatigue91.3 93.1 96.0 92.0 75.1 86.4 85.2 strength maintenance percentage (%)

It can be seen that Examples 5 to 8 exhibit superior uniformity ofphysical properties, exhibit superior fatigue resistance because stressapplied to the hybrid tire cord during repetition of tension/compressionof the tire can be dispersed to not only the aramid primarily twistedyarn but also the nylon primarily twisted yarn, in particular, exhibitsuperior fatigue resistance when tension/compression deformation isserious, and maintain superior fatigue resistance whentension/compression/shearing is repeatedly applied upon actual tiredriving.

On the other hand, it can be seen that Comparative Example 4 exhibitsuniformity of physical properties, but it is difficult to securestability of the cord because stress is intensely applied to the aramidprimarily twisted yarn upon repeated tension and compression of the tireand characteristics of the tire cord are bad. Comparative Example 5 hasa difficulty in securing fatigue resistance despite of long aramidprimarily twisted yarn, and Comparative Example 6 has covering-typehybrid properties due to excessively long aramid primarily twisted yarnand thus deterioration in uniformity of physical properties andincreased defect rate in manufacture of tires, and has post-fatiguemaintenance percentage of 90% or higher when tension/compressiondeformation is small, or exhibits great deterioration in fatigueresistance strength when tension/compression is great ortension/compression/shearing is repeated.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A hybrid tire cord comprising: a nylon primarily twisted yarn; and anaramid primarily twisted yarn, wherein the nylon primarily twisted yarnand the aramid primarily twisted yarn are secondarily twisted together,and after untwisting of the secondary twisting of the hybrid tire cordhaving a predetermined length, a length of the aramid primarily twistedyarn is 1.005 to 1.025 times a length of the nylon primarily twistedyarn.
 2. The hybrid tire cord according to claim 1, wherein the nylonprimarily twisted yarn has a first twist direction, the aramid primarilytwisted yarn has a second twist direction, the nylon primarily twistedyarn and the aramid primarily twisted yarn are secondarily twistedtogether in a third twist direction, the second twist direction is thesame as the first twist direction, and the third twist direction isopposite to the first twist direction.
 3. The hybrid tire cord accordingto claim 1, wherein the aramid primarily twisted yarn has a lower twistnumber than a twist number of the nylon primarily twisted yarn.
 4. Thehybrid tire cord according to claim 3, wherein the aramid primarilytwisted yarn has a 0.1 to 5% lower twist number than a twist number ofthe nylon primarily twisted yarn.
 5. The hybrid tire cord according toclaim 1, wherein a weight ratio of the nylon primarily twisted yarn tothe aramid primarily twisted yarn is 20:80 to 80:20.
 6. The hybrid tirecord according to claim 1, further comprising an adhesive agent coatedon the nylon primarily twisted yarn and the aramid primarily twistedyarn, wherein strength at break and elongation at break measured by ASTMD885 are 8.0 to 15.0 g/d and 7 to 15%, respectively, and a strengthmaintenance percentage after disk fatigue test conducted by JIS-L 1017of Japanese Standard Association (JSA) is 90% or higher.
 7. The hybridtire cord according to claim 6, wherein the hybrid tire cord has 3%LASE, 5% LASE, and 7% LASE measured by ASTM D885, of 0.8 to 2.0 g/d, 1.5to 4.0 g/d, and 3.0 to 6.0 g/d, respectively.
 8. The hybrid tire cordaccording to claim 7, wherein the hybrid tire cord has a shrinkage of1.5 to 2.5%, wherein the shrinkage is measured under a primary load of0.01 g/denier at 180° C. for 2 minutes.
 9. A method of manufacturing ahybrid tire cord comprising: a first step of primarily twisting anaramid filament yarn in a first direction to form an aramid primarilytwisted yarn; a second step of primarily twisting a nylon filament yarnin a second direction to form a nylon primarily twisted yarn, the secondstep and the first step being conducted simultaneously; and a third stepof secondarily twisting the aramid primarily twisted yarn and the nylonprimarily twisted yarn in a third direction to form a plied yarn, thethird step being conducted continuously with the first and second steps,wherein the first, second and third steps are conducted by one twister,the second direction is the same as the first direction, the thirddirection is opposite to the first direction, tension applied to thenylon filament yarn in the second step is higher than tension applied tothe aramid filament yarn in the first step, and the tension applied tothe nylon filament yarn in the second step is higher than the tensionapplied to the aramid filament yarn in the first step in such an amountthat the aramid primarily twisted yarn is 1.005 to 1.025 times longerthan the nylon primarily twisted yarn after untwisting of the secondarytwist of the hybrid tire cord with a predetermined length.
 10. Themethod according to claim 9, further comprising: dipping the plied yarnin an adhesive agent solution; drying the adhesive agentsolution-impregnated plied yarn; and thermally treating the dried pliedyarn.
 11. The method according to claim 10, wherein the dipping, dryingand thermal treatment steps are continuously conducted, and tensionapplied to the plied yarn in the dipping, drying and thermal treatmentsteps is 0.4 g/d or less per cord.